Ultra high frequency modulator



Aug. 24, 1948. L. D. SMULLlN' ULTRA HIGH FREQUENCY MODULATOR Filed Aug. 15, 1947 8 TEE/7M SOURCE mm L NU m m. 0 5 W L Patented Aug. 24, 1948 ULTRA HIGH FREQUENCY MODULATOR Louis D. Smullin, Nutley, N. J., assignor to International Standard Electric Corporation, New York, N. Y., a corporation of Delaware Application August 15, 1947, Serial No. 768,821

16 Claims.

This invention relates to modulator systems, and more particularly to translator systems of the type adapted to handle extremely short pulses of rapid repetition which may be derived from a nuclear energy detector.

The need often arises for providing means for determining coincidence or spacing between pulses with a very close resolution of time for example, a resolution in the order of It has been proposed to use the electron emissio from a nuclear detector as the gun for a travelling wave amplifier and to provide in the output thereof, waves that can be compared more readily with those from a second such circuit.

For the purpose of detecting and responding to pulses les than one microsecond apart silicon crystals have been proposed. These crystals however, are limited to a relatively low power level on the order of 10 milliwatts. If they are to be used in a square law region the output energy level is even less in the order of one milliwatt.

It is an object of this invention to provide a translator structure of simple construction useful for translating electron energy into a carrier frequency modulation and capable of broad band operation for the translation of pulses of extremely short duration, spaced less than 1 microsecond apart.

According to a feature of my invention I provide a high frequency oscillator and a utilization device between which is provided a branched Wave guide system forming effectively a balanced bridge. The wave guide system is adjusted substantially to produce a minimum, preferably zero output under normal conditions. In one arm of this bridge is arranged a resonant gap which may be traversed by an electron stream. Traversal of this gap by an electron stream produces an unbalance in the bridge providing an output energy for the utilization circuit.

According to a further feature of my invention the source of electrons for the electron stream may be a nuclear particle detector for example, of the electron multiplier type. Thi detector may be mounted directly on the wave guide and an opening in the covering of the wave guide may be provided for projection of the electron stream into the guide. The portion of the guide adjacent this opening may be sealed from the remainder of the wave guide and evacuated and within this sealed portion is provided a resonant gap across which the electron stream is directed. The resonant gap under normal conditions will effect a variation in impedance in this arm of the bridge. To compensate for this impedance so as to achieve a balance of the bridge, phase shifting and attenuating devices may be provided in the other arm thereof. In operation the electron stream across the gap serves to absorb energy from the source in this bridge arm resulting in an unbalance thereof and consequent modulation effects of the energy at said utilization device.

The above-mentioned and other features and objects of this invention and the manner of attaining them will become more apparent and the invention itself will be best understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawing.

Figure 1 of which illustrates diagrammatically a circuit embodying the features of my invention, and

Fig. 2 of which is a fragmentary sectional view illustrating a modification thereof.

Turning to the Fig. 1, a high frequency source is illustrated at I coupled through wave guide 2 and a coupler 3 to two branch arms 4 and 5, these branch arms being joined at their other end in a second coupler 6, and coupled over the wave guide '5 to a utilization circuit 8. The couplers 3 and 6 may be of the so-called magic tee type used with wave guides. For a more complete description of this type of coupler, reference is made to MIT Radiation Laboratory Report #643, magic tee microwave impedance bridge. In the figure a portion of wave guide 4 is shown broken away and is illustrated in enlarged sectional view, more clearly to illustrate the structure. This brokenaway portion is referred to herein as a pulse-absorber. Between the upper and lower walls 9 and l I! of wave guide 4 are provided glass partitions I I sealed to the walls so as to provide a gas-tight chamber. In upper wall 9 is provided a hole within which is fastened a. tubular protuberance I2 extending into the chamber in wave guide 9. Mounted on the lower wall It of wave guide 4 is a second protrudin element I3 which extends within the guide toward protuberance I2, providing a gap I4. Mounted on the outer surface of wall 9 is shown a pulse electron source I5 which may for example, be a nuclear energy detector of the electron multiplier type. The detector I5 is sealed to wall 9 and mounted over the opening in wall 9 so that the electron stream emitted therefrom will be directed through the tubular opening of protuberance I2 to the surface of protuberance I3. At I6 is indicated the last electrode of detector I5 and between this electrode I6 and protuberance I3 is coupled a potential source such as battery Il providing a positive potential on pro- 3 tuberance l3 to assure that the electron stream from detector IE will be attracted across the gap.

Protuberance l3 may be insulated for direct currents from the wall H] of guide 4. However, this capacity may be suificiently large as to form a very small impedance to the passage of high frequency energy. In order to neutralize the capacity loading of the guide by theprotuberances l2 and I3 an inductive iris i8, well known in the art, is placed transversely of the guide in the plane of the protuberances. In guide 5 of the bridge network are provided variablephase shifter I!) and a variable attenuator 20 which may be adjusted so that the normal output of energy from oscillator l to utilization circuit 8 is aminimum, preferably substantially zero. An additional battery 2i and leads 22 are shown connected to detector iii to indicate the usual application of potential for electron multiplying and electron generating purposes.

.In operation the electron beam directed across gap Hi will absorb energy inthe arm 4 upsetting the normal balance of the circuit and producing an output energy flow in utilization circuit 8 dependent upon the absorbing effect of the gap and related in amplitude to the stream across said gap. The electron beam across the-gap serves to produce a shunt resistance across the guide which should be as small as practically possible. The

gapsh-ould preferably be substantially resonant at the carrier radio frequency so that its effect will be more pronounced. The windows or glass partitions ll through which the radio frequency carrier passes should preferably have a loaded Q, which is less than or equal to 1. The gap itself is low Q, for example about 5.v For a maximum effect the electrons passing a gap should have a transit time of about A; of the R. F. period requiring relatively low velocity and it is contemplated that potentials of 17 to 200 volts be applied from the emitting electrode l6 across the gap. For this reason the gap itself should be relatively small in order to secure sufiicient voltage gradient.

While I have disclosed my invention as applied to a metal-covered dielectric guide in Fig. 1, it is clear that other types of wave guide may be used if desired. For example, in Fig. 2 a cross-sectional view of the wave guide t in the form of a coaxial line is shown. In this figure the outer conductor 23 and an inner conductor 2d serve to provide the normal coaxial line. At the point within the evacuated envelope ll partitions 25 are provided to secure the desired resonant cavity effect. The inner conductor M serves as a terminating or collecting electrode for the electron stream while the protuberance 2d serves as the inlet portion of the gap to permit the electrons from the source l5 to be fed therein.

It will be clear that the principles discussed in connection with Fig. 1 will apply equally well to the modification of the type shown in Fig. 2.

While I have described above the principles of my invention in connection with specific apparatus,-it is to be clearly understood that this description is made only by way of example and not as limitation to the scope of my invention.

What is claimed is:

1. A modulator for modulating radio frequency carrier energy in response to an electron stream, comprising a carrier energy source, a wave guide coupled to said source,'an evacuated .resonant gap provided in said wave guide, a nuclear par ticle detector of the electron multiplier type, and means to direct electrons from said detectoracross circuit, two parallel wave guides inter-connecting said load and said circuit, said wave guides being proportioned to provide normally a given energy output to said circuit, a resonant gap in one of said wave-guides, and means for passing said electron stream across said gap to alter the transmission in said .one Wave guide, whereby energy from said source will. be transferred to said utilization circuit.

5. A circuit according to claim 4 wherein said means comprises anelectron multiplying nuclear particle detector.

6. A. circuit according to claim 5 wherein said resonant gap is sealed in a gas-tight evacuated container from the remainder of said wave guide.

'7. A circuit according to claim 6 wherein said guides are of tubular metal filled with gas, said resonant gap comprising protuberances extending inwardly in opposite directions from :the walls of said one wave guide.

8. A circuit according to claim '7 wherein one of the protuberances of said gap is in the form of a tube the opening of said tube extending through the tubular metal wall of said guide, said detectorbeing sealed to the outer surface of said wall in substantial registry with said opening.

9. A circuit according to claim 4 comprisingan input wave guide magic tee between said source and saidparallel wave guides and an output wave guide magic tee between said parallel wave guides and said utilization device.

10. A circuit according to claim 9 further comprising adjustable phasing and attenuation means in the other of said wave guides to facilitate balance of said circuit.

11. A circuit according to claim 4, wherein at least one of said wave guides comprises a coaxial transmission line.

12. An amplifier for pulses of electrons comprising a high frequency energy source, a high frequency network comprising two wave guide branches coupled to said source and joined at their other ends, said branches being proportioned to provide normally a substantially zero energy ouput at the joined ends, an electron responsive gap, means in said guide, and means foryapplying said pulses of electrons to said gap means to-alter the transmission of said wave guide whereby a proportional radio frequency current will occur at said joined ends of said branches.

13. A wide band translator for pulses of electrons comprising a high frequency energy source, a high frequency network comprising two wave guide branches coupled to said source and joined at their other ends, said branches being proportioned to provide normally a zero energy output at the joined ends, at least one of said guides being a hollow wave guide, an electron responsive gap meansin said hollow guide, and means for applying said pulses of electrons across the gap of said electron responsive means to'alter the Wave transmission along said electric guide whereby a proportional radio frequency current will occur at said joined .ends of said branches.

14. A translator for pulses of electrons derived from a nuclear particle detector comprising a high frequency energy source, a high frequency network comprising two wave guide branches coupled to said source and joined at their other ends, said branches being proportioned to provide normally a zero current output at the joined ends, an electron responsive gap means in said one wave guide in a sealed compartment therein, and means for coupling said nuclear particle detector to said electron responsive means to apply said pulses across said gap to alter the transmission character of said one wave guide, whereby a proportiona1 radio frequency current will occur at said joined ends of said branches.

15. A translator for electron currents comprising a source of ultra, high frequency energy, an input branched magic tee coupler of the Wave guide type coupled to said source, a coupler of similar type coupled to a, utilization device, a first and second wave guide inter-connecting respective branches of said couplers, a resonant gap in said first wave guide comprising a, tubular protuberance thereinto and a terminal spaced from said tubular protuberance to provide a gap, said tubular extension extending through said wall, a coplanar inductive iris for compensating the capacitive effect of said gap, phase shift and attenuating means in said second wave guide to ,compensate for impedance effects of said resonant gap to provide normally at said utilization device substantially zero output, an electron producing nuclear particle detector sealed to the outer surface of the metallic cover of said first wave guide at a point registering with the opening of said tubular extension, means for applying a voltage positive with respect to said detector to said terminal whereby electrons will be directed across said gap upsetting the normal balance of the system, producing in said utilization device an energy level proportional to the electron current.

16. A translator for electron pulse currents from a nuclear particle detector of the electron multiplier type, comprising a, source of ultra high frequency energy, an input branched coupler of the hollow wave guide type providing transmission in given directions of energy from said source, a coupler of similar type coupled to a utilization device, a first and second hollow wave guide interconnecting respective branches of said couplers, a resonant gap in said first wave guide comprising a tubular protuberance therein and a second protuberance extending toward said tubular protuberance to provide the gap, said second protuberance being insulated for direct current from the metallic cover of said first wave guide, and said tubular protuberance extending therethrough, an inductive iris coplanar with said gap to compensate the capacitive effect of said gap, gas impervious non-reactive windows sealing said resonant gap from the remainder of said first wave guide, phase shift and attenuating means in said second wave guide to compensate vfor impedance effects of said resonant gap to provide normally at said utilization device substantially zero output, an electron producing nuclear particle detector sealed to the outer surface of the metallic cover of said first wave guide at a point registering with the opening of said tubular extension, means for applying a voltage positive with respect to said detector to the other extension whereby electrons will be directed across said gap upsetting the normal balance of the system, producing in said utilization device an energy level proportional to the electron current.

LOUIS D. SMULLIN. 

